Copy and Paste creates random null objects from existing geometry
If you want to duplicate objects in your scene, instead of using Ctrl-C to copy them, consider using Shift-D instead. Admitedly. It's a bit confusing that there are both methods available when they don't seem to completely work the same way. I don't use Ctrl-C for anything except copying poses in Pose Mode. And I have no issues. Interestingly, when I just tried to use Ctrl-C on an object in a scene, as you have done, I got a weird result also: It made an extra copy of my armature object. However, it's an armature that wasn't even part of the object I tried to copy. Very odd.